This circuit uses a transistor as a sensor and operates in the range of 0 to 50º C. We found it in old documentation. Operational equivalents can be used.
This 1950's circuit used one of the first commercial transistors and had two stages for audio...
Using integrated circuits from the time, we found this audio compressor in an English publication from...
This is an experimental crystal radio that uses no power source. The antenna must be very long (at...